1. Field of the Invention
The present invention relates to a light-emitting device, and more particularly, to a light-emitting device with compound substrate.
2. Description of the Prior Art
The applications of light-emitting diodes are extensive and include such applications as optical display devices, traffic signals, data storing devices, communication devices, illumination devices, and medical apparatuses.
Traditionally, materials of light-emitting devices are semiconductors having poor thermal conduction properties. When such a light-emitting device is turned on, the light-emitting device is illuminated and generates heat. However, a semiconductor cannot transmit heat very quickly. If the heat cannot be removed in a reasonable time, the light-emitting device will suffer decreased lighting efficiency because of the excessive heat. For a light-emitting stack layer of AlGaInP at a given operating current, if the external temperature increases from 20C. to 80C., the brightness will decrease 20%˜50%. For small-scale light-emitting devices, this problem is not serious because the operating current is low. If the operating current is smaller than 30 mA˜50 mA, the heat can be removed from the stack layer. However, in large-scale light-emitting devices where the operating current is larger than 100 mA˜1A, if the heat cannot be removed in good time, the increasing temperature will decrease the brightness resulting in low lighting efficiency.
U.S. Pat. No. 6,287,882, which is incorporated herein by reference, discloses a light-emitting diode employing a metal reflecting adhesive to bind a light-emitting unit and a metal substrate so that the light-emitting diode can reflect light and conduct heat. Taiwan (R.O.C.) patent No.151410 discloses a semiconductor element having a metal substrate and a plating method to form the metal substrate on the semiconductor light-emitting stack layer to replace the conventional semiconductor substrate to conduct heat. However, in manufacturing processes of the above two structures, it is difficult to cut the metal substrate in the subsequent process of chip cutting.